It is generally difficult to asymmetrically reduce ketocarboxylic acid derivatives represented by the general formula (1):
(in the formula, R1 is an optionally substituted alkyl group having 1 to 20 carbon atoms; Y is hydrogen or a metal) or salts thereof. For this reason, only the following methods are known as methods for producing optically active hydroxycarboxylic acid derivatives represented by the general formula (3):
(in the formula, R1 and Y are the same as described above, and * represents an asymmetric carbon).
(i) A method using an enzyme (Non-Patent Document 1, Patent Document 1).
(ii) A method using a stoichiometric amount of optically active reagent:                (a) a method using an optically active reducing reagent (Non-Patent Document 2);        (b) a method using an optically active ligand (Patent Document 2).        
(iii) A method using a catalytic amount of optically active reagent:                (a) a method using hydrogen gas and a transition metal reagent (Non-Patent Document 3).            Patent Document 1: WO 2005/049816    Patent Document 2: U.S. Pat. No. 4,614,806    Non-Patent Document 1: Tetrahedron: Asymmetry, 2004, 15(23), 3763.    Non-Patent Document 2: Tetrahedron Letters, 1998, 39, 5501.    Non-Patent Document 3: Chirality, 1991, 3(4), 370.
However, compounds that can be used in the production method (i) are limited, and this method cannot be generally used. Furthermore, the productivity of this method is typically low and there is a problem in industrial use.
In the production method (ii), an expensive optically active reagent has to be used in an amount equivalent to that of a reaction substrate and there is a problem in industrial use.
In the production method (iii), because hazardous hydrogen gas is used and a very expensive transition metal catalyst is used, there is a problem in industrial use.